The present invention relates to a plasma processing method.
When forming a specific pattern at a workpiece through plasma etching technology, a photoresist film is normally utilized as a mask. The photoresist film must be removed after the etching process under normal circumstances. Accordingly, a plasma ashing technology is proposed in the prior art as a technology through which the photoresist film is removed. A plasma ashing apparatus having an upper electrode and a lower electrode facing opposite each other inside a processing chamber is employed in the plasma ashing process. In this apparatus, high-frequency power with a specific frequency is applied to the upper electrode and high-frequency power with a frequency lower than the frequency of the power applied to the upper electrode is applied to the lower electrode. This raises the processing gas induced into the processing chamber to plasma and, as a result, the photoresist film formed at the workpiece placed on the lower electrode is removed (ashed).
However, in the ashing processing method described above, in which high-frequency power for biasing achieving a specific power level is continuously applied to the workpiece on the lower electrode, the ions in the plasma act on the workpiece to an excessive degree before the process ends. Thus, at a workpiece 10 assuming the damascene structure illustrated in FIG. 5(a), for instance, not only the photoresist film on an SiO2 film 12 constituting a layer insulating film is removed but also shoulders 14a of a via hole 14 and shoulders 16a of a groove 16 formed at the SiO2 film 12 are removed. In addition, the internal diameter of the via hole 14 and the cross sectional width of the groove 16 along the shorter side increase. This poses a problem in that no ultra-fine wiring structure can be formed at the workpiece 10. It is to be noted that a TiN film 18 and a W film 20 are formed under the SiO2 film 12 at the workpiece 10.
If, on the other hand, the process is implemented without applying high-frequency power for biasing to the workpiece unlike in the ashing method described above, the quantities of ions and radicals induced to the workpiece are reduced. Thus, the shoulders 14a of the via hole 14 or the shoulders 16a of the groove 16 are not milled and the internal diameter of the via hole 14 and the cross sectional width of the groove 16 along the shorter side do not increase, as shown in FIG. 5(b). However, there is a problem with this ashing method in that so-called fence portion 14b formed during the etching process are not removed. It is to be noted that the fence portion 14b distend from the area around the opening of the via hole 14 toward the upper portion of the groove 16. As a result, a specific wiring structure cannot be formed inside the via hole 14 or inside the groove 16.
An object of the present invention, which has been completed by addressing the problems of the technologies in the prior art discussed above, is to provide a new and improved plasma processing method which makes it possible to eliminate the problems explained above and other problems.
In order to achieve the object described above, in a first aspect of the present invention, a plasma processing method for removing a photoresist film formed at a workpiece placed inside a processing chamber by raising a processing gas induced into the processing chamber to plasma, comprising a step in which high-frequency power for biasing at a first power level is applied to the workpiece, a step in which the processing gas is raised to plasma and a step in which high-frequency power for biasing at a second power level is applied to the workpiece by switching the high-frequency power for biasing at the first power level to the high-frequency power for biasing at the second power level lower than the first power level before the photoresist film is completely removed, as disclosed in claim 1, is provided.
According to the present invention, plasma processing is first implemented by applying the highfrequency power for biasing at the first power level to the workpiece. The first power level is set so as to allow ions with a relatively high energy level to be induced to the workpiece. Thus, fence portion formed at the workpiece during the etching process, for instance, can be removed while removing the photoresist film. In addition, according to the present invention, plasma processing is implemented by switching the high-frequency power applied to the workpiece from the first power level to the second power level before the photoresist film is completely removed. The second power level is set so as to allow ions with a relatively low energy level to be induced to the workpiece. As a result, the photoresist film can be removed without affecting the lower layer structure beneath the photoresist film.
In addition, in order to achieve the object described above, in a second aspect of the present invention, a plasma processing method for removing a photoresist film formed at a workpiece placed inside a processing chamber by raising a processing gas induced into the processing chamber to plasma, comprising a step in which highfrequency power for biasing is applied to the workpiece, a step in which the processing gas is raised to plasma and a step in which the application of the high-frequency power for biasing is stopped before the photoresist film is completely removed, as disclosed in claim 2, is provided.
According to the present invention, plasma processing is first implemented by applying the high-frequency power for biasing to the workpiece. The level of the high-frequency power for biasing is set roughly equal to the first power level mentioned earlier. As a result, the photoresist film and the fence portion can be removed at the same time. Furthermore, according to the present invention, the supply of the high-frequency power for biasing to the workpiece is stopped before the photoresist film is completely removed. Thus, the energy of the ions induced to the workpiece is reduced, so that the photoresist film is removed without affecting the lower layer structure beneath the photoresist film.
In a third or fourth aspect of the present invention, a plasma processing method in which a plasma etching process is first implemented at the workpiece halfway through a specific layer by using as a mask a photoresist film having an opening pattern with a larger opening area than the opening area of a hole formed at the specific layer with the opening pattern containing the opening of the hole and then the photoresist film is removed, as disclosed in claim 3 or claim 4, comprising steps similar to those disclosed in claim 1 or claim 2, is provided.
When a plasma etching process is implemented on the workpiece, fence portion is formed around the opening of the hole. Through the process implemented by performing steps similar to those disclosed in claim 1 or claim 2, the photoresist film and the fence portion can be removed at the same time while retaining a pattern achieving a specific form.
Furthermore, it is desirable that the present invention be adopted in conjunction with a photoresist film constituting a mask utilized to form a specific pattern at an SiO2 film or an organic film formed on a workpiece, as disclosed in claims 5 or 6, for instance. When an SiO2 film or an organic film is patterned by using a photoresist film as a mask through a plasma etching process in order to achieve, for instance, a damascene structure, fence portion is formed at the pattern area. In addition, SiO2 and organic materials are easily milled by plasma. Thus, by removing the photoresist film according to the present invention as disclosed in claims 1xcx9c4, the fence portion is removed at the same time, while ensuring that any damage to the pattern formed at the SiO2 film or the organic film is prevented.